Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal; from feed stock intermediates, such as syngas; or from starchy materials or cellulose materials, such as corn and sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are often converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. It is also well known to reduce, e.g., hydrogenate, aldehydes to their corresponding alcohol. Thus, ethanol may be formed via the hydrogenation of acetaldehyde. Exemplary aldehyde hydrogenation processes are described in U.S. Pat. Nos. 5,093,534; 5,004,845; 4,876,402; 4,762,817; 4,626,604; 4,451,677; 4,426,541; 4,052,467; 3,953,524; and 2,549,416, the entireties of which are incorporated herein by reference.
As an example, crotonaldehyde may be hydrogenated to form crotyl alcohol. The following references relate to this reaction: (1) Djerboua, et al. “On the performance of a highly loaded CO/SiO2 catalyst in the gas phase hydrogenation of crotonaldehyde thermal treatments—catalyst structure-selectivity relationship,” Applied Catalysis A: General (2005), 282, pg 123-133; (2) Liberkova, and Tourounde, “Performance of Pt/SaO2 catalyst in the gas phase hydrogenation of crotonaldehyde,” J. Mol. Catal. A: Chemical (2002), 180, pg. 221-230; (3) Rodrigues and Bueno, “Co/SiO2 catalysts for selective hydrogenation of crotonaldehyde: III. Promoting effect of zinc,” Applied Catalysis A: General (2004), 257, pg. 210-211; (4) Ammari, et al., “An emergent catalytic material: Pt/ZnO catalyst for selective hydrogenation of crotonaldehyde,” J. Catal. (2004), 221, pg. 32-42; (5) Ammari, et al., “Selective hydrogenation of crotonaldehyde on Pt/ZnCl2/SiO2 catalysts,” J. Catal. (2005), 235, pg. 1-9; (6) Consonni, et al. “High Performances of Pt/ZnO Catalysts in Selective Hydrogenation of Crotonaldehyde,” J. Catal. (1999), 188, pg. 165-175; and (7) Nitta, et al., “Selective hydrogenation of αβ-unsaturated aldehydes on cobalt—silica catalysts obtained from cobalt chrysotile,” Applied Catal. (1989), 56, pg. 9-22.
Several references have also described combining an acetic acid production facility with an ethanol production facility. EP02060553 describes a process for converting hydrocarbons to ethanol involving converting the hydrocarbons to ethanoic acid and hydrogenating the ethanoic acid to ethanol. The stream from the hydrogenation reactor is separated to obtain an ethanol product and a stream of acetic acid and ethyl acetate, which is recycled to the hydrogenation reactor.
WO2009063176 describes a process for the production of ethanol from a carbonaceous feedstock, wherein the carbonaceous feedstock is first converted to synthesis gas which is then converted to ethanoic acid, which is then subject to a two stage hydrogenation process by which at least a part of the ethanoic acid is converted by a primary hydrogenation process to ethyl ethanoate, which ethyl ethanoate is converted by a secondary hydrogenation process to produce ethanol.
U.S. Pat. No. 7,884,253 describes a process for selectively producing ethanol from syngas. The process deliberately introduces H2 into the carbonylation step to encourage a partial reduction of the carbonylated product to form a mix of acetaldehyde and ethanol. The mix is reduced to ethanol and water that can be distilled.
The need remains for improved processes for recovering ethanol from a crude product obtained by reducing alkanoic acids, such as acetic acid, and/or other carbonyl group-containing compounds.